Koponop

So I've managed to source a spare instrument cluster and plugged in the connectors. All appears to be functioning properly, especially the fuel gauge. Just to satisfy my curiousity I've taken voltage readings at the fuel and temperature gauges. Both indicate 7.95 at one pin, the temperature gauge reads 5.56 at the second pin and reduces as the engine warms. The fuel gauge reads 3.56 at the second pin as opposed to the 0.8 reading on the original cluster. The yellow wire going to the sender also reads 3.56 with the sender connected. I surmise that the voltage at the second pin of the fuel gauge should always correspond to the yellow wire and the fact that the second pin voltage was previously so low was the reason for the needle reading full. The problem would appear to lie somewhere between the yellow wire and the second pin of the gauge as the yellow wire previously had been reading 3.46 and the second pin 0.8. The cause of the discrepancy is a mystery to me and will remain so as I have no desire or need, (fingers crossed), to investigate further. Hopefully this topic may help someone in diagnosing a similar problem and many thanks to those who contributed - especially Papez, as I see your last post just appeared. Cheers, Kieran

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Managed to take a screenshot of the pdf. Hopefully this will be accessible.

Very frustrating that some members have more difficulty than others with opening files. Is this a browser problem or a host issue? How do we get around this ?

Ah, you're right Nigel. The file won't open for me either so I've saved it again as an oxps. Here goes again. Caddy Dash Panel.oxps

My understanding is that the lamp is actually operated by the gauge and not directly by the float. However the float must regulate the resistance going through the gauge which in turn provides sufficient earth / ground to illuminate the lamp?

The diagram I have is the attached pdf file which I downloaded from Erwin. Hopefully you can open it? Any thoughts greatly appreciated. Caddy Dash Panel.pdf

Thanks Nigel. Rest assured I have already been through all the basics, the sender unit taken out & tested (10 - 160 ohms), the wiring to & from the sender (yellow positive in & blue negative out), the blue connects to a brown before making a verified earth, the yellow is verified intact at it's connection to the PCB i.e. the solder behind the 10 point connector block. So I've ruled out the sender & all the wiring which is why I'm now concentrating on the PCB (which I believe can be somewhat suspect on these models). I have the wiring diagram for the instruments which indicates that the power supply for the fuel gauge is via a voltage stabiliser. My reading of the diagram is that this power then flows through the low fuel warning lamp (in series), then to the fuel gauge, then to the yellow wire which goes to the sender which then supplies varying degrees of earth resistance depending upon the float position. At empty the resistance becomes low enough to illuminate the warning lamp. Although I've been chasing after the voltage stabiliser I have no confidence that it would provide the answer as I can measure 12v at both sides of the low warning lamp which would be correct for proper illumination. So I will eliminate the stabiliser as a suspect. I have already replaced the gauge itself but with the same result - always full. I am reading 7.93v at one side of the fuel gauge which coincides with one side of the temperature gauge. The same 7.93v also goes to the yellow wire for the sender so long as the sender is disconnected but this drops to 3.46v when the sender is connected, presumably due to the resistance within the sender.The other side of the fuel gauge reads 0.8v which appears quite low in comparison with the other side of the temperature gauge which reads about 5.5v when cold while dropping to about 4.5v as the engine warms and the hand rises. I now wonder if the low voltage on the other side of the fuel gauge is the cause of the hand reading full. This will be the focus of my investigation going forward and I'll post my findings in due course.

Cheers for that, Nigel. I currently have the instrument cluster removed and all 4 clocks separated from the PCB. Now I'm trying to check the PCB for defects but, as yet, have found none. Obviously there are numerous components attached to the PCB and I'm wondering if one of them is the voltage stabiliser or is it mounted separately from the PCB. Unfortunately I have no idea what it looks like which doesn't help matters. Do you have or know of an image which shows the voltage stabiliser? Many thanks, Kieran

Nigel, I'm still no further forward with this but I saw on another post you had mentioned a potential cause could be an issue with the voltage stabiliser which sounds logical to me. Do you know where I can locate the stabiliser itself, what it looks like and what readings I should find on it? Thanks, Kieran

Thanks for the reply, Nigel. This is the chart I tried to attach.

New to the forum and have seen this subject discussed already but unfortunately some time ago so that some images are no longer available. Anyway, the title is self explanatory but the problem began just recently, one day apparently working fine and then suddenly registering full, even with the sender disconnected. I've attached a chart of voltage and resistance readings taken from the cluster under various conditions which I hope may help to throw some light on the cause of the problem. Any help or suggestions greatly appreciated and feel free to query my amateur terminology. Thanks. Caddy Fuel Gauge Analysis 250629.pdf